We can all tell whether something is pressing down on our skin, brushing it or twisting against it -- but it's not so easy for a robot or other inanimate objects to figure these things out.

A recent breakthrough could make that possible, however.

A new type of hairy electronic skin could soon make robots adept at feeling a slight breath of air or the faint beatings of a heart. This new sensor, which is even more sensitive than human skin, could have wide applications in prosthetic limbs, heart-rate monitors and robotics.

Kahp-Yang Suh and colleagues at Seoul National University in South Korea were inspired to create the flexible touch sensor by beetle wing-locking structures, which are composed of two layers of interlocking hairs, much like two hair brushes meshed together. (See figure.)

the 'hairs' are sheets of polymer fibres that are 100 nanometres in diameter and one micrometre long, and coated with metal to make them electrically conductive. When the sheets are sandwiched together, the nanohairs are attracted to one another and locked in .... The device is then wired up so that an electrical current can be applied, and covered in a layer of soft, protective polymer.

In the figure above, different types of forces -- direct pressure, shear forces and torquing forces -- move the hairs in a different ways, and Suh's device can analyze how the hairs respond during the force and recover afterward to discover what kind of force it was.

So far, 10,000 test cycles show that the sensor can detect the motion of a tiny water droplet and the force of a heartbeat.

The sensor could be useful for robots that interact with people to get tactile input. Cameras, which provide visual information, can get blocked and overloaded with information. Tactile sensors, on the other hand, only collect data when they are touched, not constantly.

The other challenges of developing robotic skin have been the need to make it flexible, in addition to sensitive and durable. It needs to be made in very large sheets; Suh says large molds could make it easy to manufacture large sheets of his sensor.

Suh says that his group is in talks with a health care company to use his sensor in heart monitors.